Referring to FIG. 1, a conventional lens assembly includes a lens barrel 4 and a plurality of optical members 5. The lens barrel 4 extends along an axis (B) includes a peripheral wall 41 that surrounds the axis (B), and has a first end 42 that is adjacent to an object side of the conventional lens assembly and a second end 43 that is opposite to the first end 42 and adjacent to an image side of the conventional lens assembly. The peripheral wall 41 defines an accommodation space 411 that is configured as a series of accommodation sections 44. The accommodation sections 44 have circular sectional dimensions, which are defined by the peripheral wall 41, and which gradually increase from the first end 42 to the second end 43 of the peripheral wall 41, and respectively serve to receive the optical members 5. The optical members 5 include a plurality of lenses 51 and at least one retaining member 52. Referring to FIG. 2, in another conventional lens assembly, the optical members 5 include a plurality of lenses 51 and at least one spacing member 53. For the abovementioned conventional lens assemblies, the optical members 5 have to be disposed in the accommodation space 411 sequentially from the first end 42 to the second end 43, and adhesive-dispensing and photocuring steps have to be performed after each of the optical members 5 is disposed in the accommodation space 411. Hence, the assembly procedure of the conventional lens assemblies is complicated and time-consuming.